A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may for example project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.
The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features which can be formed on that substrate. A lithographic apparatus which uses extreme ultraviolet (EUV) radiation, being electromagnetic radiation having a wavelength within the range 4-20 nm, may be used to form smaller features on a substrate than a conventional lithographic apparatus (which may for example use electromagnetic radiation with a wavelength of 193 nm). A free electron laser may be used to generate EUV radiation for use by a lithographic apparatus.
A lithographic system may comprise one or more radiation sources, a beam delivery system and one or more lithographic apparatus. The beam delivery system of a lithographic system may be arranged to direct radiation from the one or more radiation sources to the one or more lithographic apparatus. It may be desirable to control the power of radiation received by a lithographic apparatus.
It is an object of the present invention to obviate or mitigate at least one problem associated with the prior art.